The glass syringe and rubber stopper have for years provided an ideal drug storage closure having unique properties of impermeability to oxygen, low extractables, biocompatability, durability, etc. However, they are both formed by processes that do not lend themselves to tight geometrical tolerances. For instance, the syringe flange is formed when a glass tube is heated to a soft state and the edges pressed over to form an edge. Typical tolerances for the inside length of a syringe or the length of a stopper are both +/−0.5 mm. The finger flange thickness has a similar tolerance. Furthermore, tight tolerances were not originally needed by these devices because they were not used mechanically with other devices. Existing passive anti-needle stick safety devices for prefilled syringes must mount to the syringe but not interfere excessively with the force required to move the plunger rod during injection nor prevent the full travel of the plunger rod, which terminates when the stopper reaches the distal end of the inside of the syringe. The safety mechanism necessarily must be triggered toward the end of administration of the drug (near the end of the plunger rod travel). However, since virtually all safety devices locate the syringe against the safety device at a point under the syringe finger flange, a stack up of worst-case tolerances can put the required plunger rod travel variance at +/−1.5 mm, when considering the tolerances of the inside length of the syringe, syringe flange thickness, and stopper length (syringe manufacturers reference the syringe inside length from the proximal end of the syringe, not the distal underside of the finger flange). Accommodating the 3 mm plunger rod position variance is very difficult for safety devices and it is desirable to reduce and or eliminate any dependence of the safety device on the syringe and stopper tolerances.